This invention relates to non destructive interrogation techniques. More particularly, it relates to a deuterated paper currency and an x-ray interrogation of the currency to detect large concentrations of cash.
Illegal drug transactions are primarily for cash. Banking laws make it difficult, at least in the United States, to use the cash to hide its illegal origins. As a result, the illegal drug trade relies on the cash receipts from the sale of drugs to be smuggled out of countries with strict banking laws. Since drug sales usually involve currency notes of small denomination, the transfer of large amounts of money, e.g. more than $100,000, and certainly any shipments of $1,000,000 or more, the bulk of the cash to be smuggled becomes sizeable. For example, $1,000,000 in $20 notes, the most common denomination of U.S. paper currency used in illegal drug trafficking, is 50,000 notes each weighing about 1.1 g. The total weight of the $1,000,000 is then about 55 kg (121 pounds).
While the broad concept of tagging currency so that large concentrations of it can be detected is straightforward, its implementation is not so straightforward since any tagging must meet a variety of other criteria. It must be totally safe. There should be no radiation. The currency should not be a health hazard even if ingested. The tagging method must work at a comparatively long range so that standard overseas shipping containers (usually having an eight foot width) can be interrogated as well as smaller items such as luggage. The system should not be readily evaded by shielding. If shielded, the shielding itself should be readily detectable. The technique should not alter or injure the currency. The tagging should also not be detectable in low concentrations of money so that legitimate interests in privacy are not invaded. The tag should also be secure against removal. The tag and its associated detection equipment should also be cost effective.
Some possible non destructive tagging systems are enumerated in the discussion of the prior art in U.S. Pat. No. 4,251,726 to Alvarez. They include conventional x-ray scanning, barium tagging, nuclear magnetic resonance, vapor tagants, and chemical tagging. In general, however, simple shielding can foil these approaches, whether by blocking interrogating electromagnetic radiation or by trapping gases at the tagged article. None are suitable for use with currency. Conventional x-ray scanning equipment as used at airports will not reliably detect hidden bulks of ordinary paper currency.
The Alvarez patent itself discloses a method for tagging explosives. Alvarez teaches partially replacing hydrogen in the explosive with deuterium or beryllium. A linear accelerator produces a beam of 2 to 4 MeV x-rays arranged to interrogate luggage moving past the beam on a conveyor. These elements undergo a nuclear reaction, absorbing an x-ray photon and emitting a neutron. A boron triflouride neutron detector is able to distinguish the presence of neutrons from a deuterated explosive, if there are about 10.sup.23 deuterium atoms, or 0.3 gram, present in the explosive. Alvarez teaches that this level of deuteration is equivalent to a level twenty times that of enriched heavy water.
While this arrangement avoids the shielding drawback of barium tagging, it also alters slightly the chemical properties of the explosives. To the best of applicant's knowledge, the Alvarez system has not been in fact used because of these concerns with these changes in chemistry. Moreover, heretofore, there has not even been a suggestion that deuteration can or should be applied to control or monitor the movement of currency. One reason is the obvious hazards of x-rays and the creation of nuclear reactions in an item in wide public circulation. Another problem is that even if currency were fully deuterated, a prohibitive process for economic reasons alone, it is rare that there will be an accumulation of currency sufficient to be detectable. In sum, to date there is no known way to detect large amounts of cash concealed in shipping containers other than through a search of the container, which may destroy the container, and in any event would be impractical for routine screening of all containers moving out of country through standard commercial shipping channels.
It is therefore a principal object of the present invention to provide a new paper currency and an associated method for detecting paper currency reliably in large concentrations, while leaving the currency substantially undetectable in low concentrations.
Another principal object is to provide such a paper currency and associated method that is reliably effective at ranges that allow the interrogation of all standard shipping containers.
Still another principal object is to provide the foregoing advantages while introducing no safety hazard, such as radioactivity and toxicity if ingested.
A further object is to provide the foregoing advantages while also being substantially impervious to shielding, and if shielded, requiring shielding that is itself readily detectable.
Another object of the present invention is to provide a tagging method that does not alter or detract in any significant way from the desirable attributes of known paper currencies.
Yet another object is to provide the foregoing advantages at an acceptable cost using known equipment.